Motor accelerating control system



Nov. 12, 1935. I I 1..' RQUARLES 2,020,961

MOTOR ACCELERATING CONTROL SYSTEM Filed June 10, 1932 3 Sheets-Sheet 1 fzg' WITNESSES: INVENTOR LaWrenceE Now 12,1935. L. R; QUARLES 7 2,

lo'roa ACCELBRATING common SYSIEI Filed June 10, 1932 3 Sheets-Sheet 2 INVENiOR lawencefiaqrhs.

Nov. 12, 1-935. L. R. QUARLES 2,020,961

MOTOR ACCELERATING CONTROL SYSTEM Filed June 10, 1932 I5 Sheets-Sheet 3 i Aawrence/fi? Qwr/es,

- v ATTORNEY Patented Nov. 12, 1935 f I ITED STATE Home accma'rmo common svs'rm Quarles, to Westinghouse Electric Iii Mann! Company, East Pittsburgh, 2a., a

of Pennsylvania Application June 10, 1932, Serial No. 616,480

11 Claims. (Cl. ire-ass) My invention relates generally to control systems and vmore particularly to control systems that may be utilized for operating electric motors.

An object of my invention is the provision of a control system of the class indicated that shall be simple and reliable in operation and be readily and economically manufactured and installed.

Another object of my invention is to control the acceleration of a direct current motor when 001k nected to a source of alternating current by the use of electronic discharge devices also interconnected with the source of alternating current.

A further object of my invention is to provide for controlling the acceleration of an electric motor without the use of accelerating contactors. I I

A still further object of my invention is to auto I maticaliy and in a continuous manner accelerate :gfieiectric motor from rest to any preselected Another object of my invention is to prevent the acceleration of a motor to a selected speed faster than a predetermined rate and thereafter to'vary the speed of the motor as desired.

Additional objects of this invention and the novel and useful features thereof will become more apparent from a study of the following specification particularly when such study is made in con- Junction with the drawings accompanying the specification and, in which: A

Figure 1 is a diagrammaticview of a control system embodying features of my invention;

Flgs.2,3and4arediagrammaticviewsofothercontrol systems that embody modifications of the features of my invention;

Fig.5isagraphicalrepresentationoftheelectricalcharacteristicsofapowergas-filledgrid controlled tube in which the shaded portion'indithe time the current is flowing between f, e anode and the cathode at a definite phase dangle betweenthe potential of the anode and the rid; a. Flg.6isasimilarg raphicalrepresentationof the electrical characteristics of a power gas-filled ,grid controlled tube inwhich the relatively small bined operation of two tubes; and

Figs. 8, 9 and 10 are graphic of the successively larger voltage values that are impressed in infinitesimal increments, on'the motor tobe erated. y With partic reference to Fig. 1, my invention comprises, in general, a motor I having a field winding 2, a transformer 3 having a primary winding 4 and a secondary winding 5. The field winding 1 may be energized from suitable direct current buses Q-and l or, what will be more pref- 5 erable when only alternating current is available, may be energized from alternating current buses 0 and I through suitable asymmetric units or rectifiers connected intermediate buses l and 9 and buses 0 and l. A pair of gas-filled grid controlled n tubes ll and Ii are provided for connecting the armature I! of the motor i in circuit relation with the secondary winding 5.

To energize theunits and circuits to which reference has just been made, suitable switches, not I shown, are provided intermediate the power station and the busesl'and 9. A bridge'phase-shifting circuit ll is provided for shifting the phase angle of the gridpotentials of the gas-filled sl'ld' controlled tubes l0 and II" relativeto their reso spective anode potentials.

"rho-power tubes Ill and II' are essentially gasfilled grid-controlled gaseous discharge tubes and comprise, respectively, anodes II and It, and cathodes or filaments I1 and II, which are generallycalled the conducting electrodes", and grids II and Il, which are usually termed the control electrodes. Inasmuch as power grid-glow tubes have the property of rectifying alternating cur-' rent, I provide for utilizing two in order to give double-wave rectification. However, it will be readily understood that myinvention is operable byusing only one grldmntiolled tube.

The power tubes II and II 'are preferably, of the well known type wherein the cathode comprisesafilamentsun'oundcdhyaninertgas. The filament when electrically heated by atsuitable source of current, liberates primary electrons which are necessary for the functioning of the ,tube. When a potential difference-is applied be- 40 control the value of the anode-cathode potential at which the gas becomes ionized, or at which an arcisformedforthcpassageofacurrent between the anode and cathode. For convenience, and in accordance with engineering parlance, the potential of the grid will hereinafter be considered with reference to the potential of the anode. For a given anode potential, there is a definite critical grid potential at which ionization occurs, thus allowing the tube to pass current in the form of an electric arc. (See Figs. 5 to 10, inclusive.)

If the potential of the grid is below this critical grid potential, no discharge occurs, and accordingly, no current passes between the anode and the cathode. 3n the contrary, if the potential of the grid rises above the critical grid potential, even if only for a moment, a discharge immediately occurs and current passes in the form of an electric are between the anode and cathode. After the arc is started, the ionized gas prevents the formation of a space charge and the arc is continued. Consequently, the grid of a gaseous discharge tube is effective only in preventing or initiating an arc, but is not effective to extinguish the are after it has once been started. The grid,

however, regains control if the flow of current between the anode and cathode ceases momentarily thus allowing the gases to deionize. Therefore, by applying an alternating current voltage to the anode and cathode, the grid has an opportunity of regaining control once every cycle and can delay the starting of an arc for as long a time during the cycle as the potential of the grid is below the critical grid potential.

For the current control of grid-controlled gasfilled tubes, three fundamental methods, well known in the art, are available. In the first or magnitude method, the phase relation of the grid potential relative to the anode potential remains fixed, but the magnitude of the grid potential varies relative to the anode potential to thus control the current that may pass between the anode and the cathode. shifting" method, the magnitude of the grid potential remains substantially fixed relative to the anode potential, but the phase relation of the grid potential relative to the anode potential is shifted thereby controlling the current passing between the anode and the cathode. The third method embodies a combination of the "magnitude" and phase-shifting" methods. In the practice of my invention, I prefer the phaseshifting" method.

When using the phase-shifting" method to control the grid potential of a tube or tubes utilized to control the speed of a direct current motor supplied with energy from a source of alter-' nating current, a severe duty is imposed on the tube or tubes particularly when the motor is starting. This severe duty, or dangerous, or tubedestroying demand on the tubes is especially serious when the armature circuit of the motor and associated control circuits are set to apply full voltage to the motor. It is, therefore, very desirable to have some automatic, yet simple. means of accelerating the motor slowly, thus preventing excessive current on the tube before all parts to be heated have attained the normal operating temperature.

The protection to the tubes and the slow automatic acceleration of the motor may be accomplished by slowly shitting the phase relation of the grid potential regardless of the final speed setting of the main speed control.

One method for accomplishing the desirable results just pointed out and the arrangement of means are shown by the bridge or phase-shifting In the second or phasea resistor 2| connected directly across the alternating current supply lines 8 and 9 and a reactor 8 I, a variable resistor-or main speed control means 22, and automatically operable circuit arrangement 23, all connected in series, but connected in 5 parallel to the resistor 2|. The primary winding 26 of a transformer 34 is connected intermediate the junctions 38 and 48. The junction 39 is positioned at the midpoint of the resistor 2|, whereas the junction I is positioned intermediate the 10 reactor 8| and the adjustable main speed control resistor 22 and the circuit arrangement 23 connected in series circuit relation.

The circuit arrangement 23 includes four rectifiers 24, 28, 29 and 38 connected as shown so that current will tend to flow through the vacuum tube 82 in only one direction. For one half of a cycle current will tend to flow from conductor 8 through the reactor 8|, adjustable main-speed-control resistor 22, rectifier 24, anode 25, past grid 26 to cathode 21, and rectifier 28 to conductor 9 and during the second half of the cycle current will flow from conductor 9 through rectifier 29, anode 25, past grid 26 to cathode '21, rectifier 30, resistor 22 and reactor 8| to conductor 8. When the conductors 8 and 9 are first energized, i. e. the line switches, not shown, are closed the grid, being connected between the high resistance resistor SI and the condenser 32 will be negatively charged and in consequence substantially no current will 30 pass through tube 82. It will be noted that the negative terminal of the battery 83 is connected to the condenser 32 thus assuring a negative bias of the grid the instant the line switches are closed to energize conductors 8 and 9. 35

With each cycle of the alternating current the grid 2 6 becomes more and more positively charged and the result is that the tube 82 passes more and more current until eventually when the condenser 82 is completely charged the resistance of the tube circuit is very low. Since the primary of transiormer 34 is connected at the mid-point I! of resistor 2| and at the junction 40 any variation in the eifective resistance below the junction II will shift the phase relation of the voltage in conductors 83 and 8|, the conductors connected to the grids l8 and 28 of the tubes l8 and II, respectively, relative to the voltage in conductor 88. Since conductor 38 is connected to the midpoint of transformer secondary 85 and since the anodes ll and I8 are connected to the terminals of the secondary 5 of transformer 3 the voltages on anodes l5 and I6 and cathodes l1 and I8 will always be in phase. Any selected shift of the phase relation of the grid potentials I8 and 28 will cause these tubes to break down at any desired point of the cycle. The total result is that the gradual charging of condenser 82 causes tubes l8 and II to break down sooner during each cycle so that the voltage impressed on the motor may range from substantially zero to full voltage as determined by the magnitude of both halves oi the wave, as may be readily apparent from a comparison of Figs. 8 to 10, inclusive.

It should be remembered though that when condenser 32 has become completely charged the final speed of the motor may not be determined by the curve shown in Fig. 10, but will depend on the setting of the movable conductor 31. The position of conductor 31 determines the speed setting of the motor I, and when the motor has accelerated in the automatic mannerprotecting tubes l0 and II and the motor-the speed of circuit l3 shown in Fig. i. 'I'hiscircuit comprises the motor may be controlled as desired by manipulation of conductor 31 with reference to resistor 22.

a Therefore, when the phase-shifting circuit has gone through its entire cycle of operation, the

phase relation between the grid potential and the anode potential is relatively large, with the result that any one of the power grid-controlled tubes passes current during substantially the entire positive half cycle. Since two tubes are used the voltage impressed on motor I will be of the character shown in Fig. 10, was a practical proposition, in view of the inductances of the circuits,

substantially a direct current voltage having but slight variations is impressed on the motor I.

The transformer 3 may be of any well known design, andif desired a plurality of secondary windings may be provided for heating the filaments I1 and I8.

Since the method of heating the filaments I'l circuit relation with one terminal of the armature I2, whereas the other terminal of the armaondary 5. In view of the fact that gas-filled grid controlled tubes operate as rectifiers in a:

wellknown manner unidirectional current is supplied to the armature I2. Since the nature of the unidirectional current is determined by the positive bias of the respective grids I9 and 20, the acceleration of the motor I may be controlled uniformly in a manner pointed out.

Consider Figs. 5, 6 and '7 which represent by curves how the change in the grid potential relative to the anode potential varies the amount of current passing between the anode and the cathode. Referring particularly to Figs. 5, 6 and 7, the higher substantially sinusoidal wave or curve represents the anode potential and the lower substantially sinusoidal, wave or curve represents the grid potential, and the concave-shaped curve represents the critical grid potential. So long as the grid potential is below the value of the critical grid potential no are between the anode and the cathode is formed for passing current. As soon as the value of the grid potential rises to, or above, the critical grid potential ionization occurs at the point wherethe grid potential curve intersects the critical grid potential curve and an arc isiormed for passing current between the anode and the cathode for the remaining anode andcathode from a minimum to a maximm by merely shifting byinfinitesimal steps the'phase of the grid potential relative to the anode potential.

Fig. 'I shows more in detail the total efiectof the operation of the tubes II and II on the armature current. While each tube is in eflect separately controlled the curves are, as shown, two

' which the grid potential effects or permits a independent operations but the current passing a in the armature circuit will nevertheless be represented by thecurrent wave designated by Since the potential drop across tubes III' and II is relatively small, a voltage as 5 the result of half the secondary winding 5 of the transformer 3 will be impressed on the armature during each half cycle. The length of time the voltage isapplied depends upon the point at break down of the tube and may be represented by BE and F1, 1. e., the angle or shift of phase between the anode potential and the grid potential.

The inertia of the armature and the inducl5 tance of the armature and associated circuits will in fact prevent the armature current from taking the theoretical characteristics shown in Figs. 8, 9 and 10. The ripples will be smoothed out very materially. The feature of importance, however, is that the voltage impressed on the' armature I! of the motor I will vary from a small value in one direction to the full operating voltage in the same direction during an interval of time determined by the characteristics oi the phase shifting circuit II and that such variation will proceed automatically, gradually andcontinuously, i. e.,- without any abrupt step by step changes. Figs. 8, 9 and 10 show curves JKLMNOPQR, J'K'LIM'N'O'P'Q'R, etc., which illustrate how the voltage on the armature I2 is varied automatically by the automatic operation of the phase shift circuit I3 heretofore explained.

In the modifications shownin Figs. 2 to 4 inelusive like elements have been given the same reference characters. The detailed description preceding thus applies equally well to these modifications except insofar asdetails of the phase shifting circuit work differently.

In Fig. 2 a pair of vacuum tubes are used to ,eifect double wave control. It is obvious that for one half cycle current willflow through resistor 42, rectifier l3, condenser 44, battery and for the other half it will flow through resistor 45, rectifier 41, condenser 48 and battery 49.. As the 45 condensers 4 4 and 8 become charged more and -more, more current passes from the anodes 5| and 58 past grids Hand to cathodes 50 and 54. The motor I may thus be automatically accelerated to the speed determined by the adjustable 50 resistor 22. It should be noted that a condenser ll is used instead of a reactor. The final result is not affected by such change.

In .the modification shown in Fig. 3 a pair of 'gas-filled grid-controlled tubes are utilized in- 5 stead of vacuum tubes and a resistor 58 is utilized. In this modification as the condensers 56 and 51 became charged the positive bias of grids 60 and El will be brought to a critical valueafter some time and the tubes will break; down, passing current from anodes Cl and 62 past the grids 60 and 84 to the cathodes 59 and 63. The acceleration of the motor thus proceeds automatically during a given time as if controlled by a one step-timelimited-contactor. In the modification shown in Fig. 4 a reactor and variable resistor are again utilized as in. the

' modification of Fig. 1 but onlyone rectifier and one vacuum tube is utilized. After switch 65 is closedcurrent for each succeeding positive cycle passes from conductor 8 through variable resistor 2!,switch 65, reactor III, battery III having a voltage high enough that the negative cycle does not permit a tendency of a reverse current,

resistor 11, rectifier I2, condenser 13, and battery 7 14 to the conductor 9. As the condenser becomes charged the grid 16 becomes more positively charged with the result that more and more current passes from the anode ll to cathode is thereby shifting the grid bias oi tubes II and H to accelerate the motor i.

From the foregoing discussion of the various modifications it is obvious that the "phaseshifting circuits are essentially Wheatstone bridge arrangements wherein one pair 01 the two legs that are connected in series have equal impedances or, in some cases, resistances, whereas the other two legs that are connected in series are provided with means for manually varying the impedance of one leg as desired and are provided with time-limit means associated with the other leg to vary automatically and in a gradual and continuous manner the impedance a substantially fixed amount during a predetermined interval of time. The voltage variations thus effected at the terminals of the Wheatstone bridge not connected to the source of energy are utilized to control the operations of a motor. The controlling efiect in the modifications shown is through a pair of gas-filled grid-controlled rectifying discharge tubes, but this invention is not limited to such arrangement. In fact, the

control of the motor may be directly from the terminals of the Wheatstone bridge.

I am aware that other circuit arrangements may be devised by those skilled in the art once having had the benefit of the teachings of this invention. My claims are therefore not to be limited to the specific details herein disclosed but I intend that my claims be given only such limitations in scope as are required by their respective terms and the prior art.

I claim as my invention:

1. A system of control for a motor, in combination, a source of electrical energy, a motor, speed control'means adapted to vary the speed of the motor over a predetermined range, control thermionic means having a cycle of operation that is completed within any predetermined interval of time and thermionic means, responsive to said control thermionic means, adapted to accelerate the motor to a speed selected by said speed control means.

2. A control system for an electric motor, in combination, asource of energy, a motor, means for connecting the motor to said source, a control electronic tube, means for varying the operating characteristics of said tube during a definite time interval, means controlled by said tube for gradually and automatically varying the voltage applied v to the motor during said time interval and means for manually controlling the speed or the motor.

3. In a system of control for a direct current motor supplied with energy from a source of alternating current, in combination, a pair of grid-controlled tubes, having anodes, cathodes and grids, respectively, for supplying direct current to the motor, a time-delay circuit for shitting the phase relation of the voltage or the grid with reference to the cathode a predetermined angle in a predetermined time, whereby the motor is automatically accelerated to a selected speed in a definite time interval.

4. In 'a control system for an electric motor, in combination, a grid-controlled tube, having a grid, an anode and a cathode, adapted to vary the energy application to the motor from a given minimum to a selected maximum, timelimit'means controlling such variations to take place during v a definite interval or time. and

further means controlling said tubes to vary the energy applications at will during operation or the motor.

5. In a control system for an electric motor, in combination, a source of alternating current, a 5 motor, a gas-filled grid-controlled tube for supplying varying amounts 01' direct current to said motor from said source of alternating current, and time limit means for changing the operating characteristics 01' the said tube by a predetermined amount during a predetermined interval citime.

6. In a control system for an electric motor, in combination, a source of alternating current, a motor, a gas-filled grid-controlled tube for supplying varying amounts of direct current to said motor from said source of alternating current, time limit means for changing the operating characteristics of the said tube by a predetermined amount during a predetermined interval 20 01' time, and speed control means for changing the operating characteristics oi said tube, at will during motor operation.

7. A control system for an electric motor comprising a motor, a thermo-electric timing means, control means for varying the time constant 01' said timing means, and means responsive to said timing means and to said control means to' respectively accelerate said motor to a speed during a time determined by the time constant of said timing means and to control the speed of the motor.

8. In a control system for an electric motor comprising, a source of alternating current energy, a direct current motor, a grid-controlled tube tor supplying direct current to said motor from said source of alternating current energy,

a phase-shifting circuit for said tube whereby the speed of the motor may be varied at will, and a timing circuit for controlling said phase-shifting circuit to accelerate the motor to a given value.

9. In a system of control for a motor, a source of alternating current, a resistor connected to be energized by said source, a reactor, a variable reslstor and a timing circuit, all connected in series in the order named, connected in parallel circuit relation to said resistor, a control transformer primary having one terminal connected to the mid-tap of said resistor and the other terminal connected intermediate the reactor and the variable resistor, a pair of grid-controlled tubes having grids, anodes and cathodes, a motor, a secondary of the control transformer having its outside terminals connected to the grids of said tubcs, circuit connections for interconnecting one to terminal 01' the motor with the cathodes and the other terminal with the mid-tap of the transformer and means for energizing the anodes of the tubes.

10. In a system of control for a motor, a source of alternating current energy, a resistor connected to be energized from. said source, an impedance, a variable impedance, and a timing circuit, all connected in series circuit relation, connected in parallel to said resistor, a motor, grid-controlled tubes for cont-rolling the motor, a control transformer having the end terminals of its primary connected respectively to the mid-tap oi the resistor and intermediate the impedance and variable impedance and the end terminal of the secondary connected to the respective grids of the tubes, circuit connections for connecting the mid-tap oi the secondary ot the control transformer to he cathodes oi the tubes and one terminal oi the armature and means for interom- I5 necting the anodes and other motor terminals with said source of energy.

11. In a control systemior controlling the speed of a motor by a grid-controlled tube, a motor, a source of energy for energizing the motor, a phase-shitting arrangement comprising, a main resistor, a condenser, a variable impedance and a circuit arrangement adapted to automatically change its effective impedance a predetermined amount during a substantially definite time interval, said condenser, variable impedance and circuit arrangement being connected in parallel to said main resistor, an electric control device having a plurality of circuits one of said circuits being connected between the mid-tap of the main resistor and a point intermediate the condenser and variable impedance and other of said circuits being interconnected with the grid of said tube to control the potential oi the grid.

12. In a control system for controlling the operations of a motor, a Wheatstone bridge, a motor, a source of electrical energy for energizing the motor and disposed to be connected to two junctions of the bridge, a control circuit arrangement connected to other two junctions, the relative im-.

pedances of the legs of the bridge being such at the instant energy is supplied to the first named junctions that substantially no current flows in said control circuit arrangement, an electrical automatically operable timing circuit for changing the impedance in one leg'of the bridge a predetermined amount during a definite interval of time to increase the current flow in the control circuit a given amount during such interval of time, means associated with the leg in series with the leg provided the timing circuit for manually varying the impedance of said leg, and means responsive to the current characteristics in the control circuit arrangement for controlling the operation of said motor.

13. A system of control for a motor, a source of power, a motor, a Wheatstone bridge having two of its terminals connected to the source of power and having two of the legs that are connected in series of equal impedance, the other two legs that are connected in series having respectively manual means for varying the impedance of one leg and automatic time-limit means for varying the impedance of the other leg a selected amount during a substantially fixed interval of time, means for energizing said motor from said source of power, and means responsive to the potential variations effected at the other two terminals of the bridge to control the energimtion of said motor.

14. A system of control for a motor, a source of alternating current energy, a direct-current motor, a grid-controlled tube having a grid, an

. ried to control the speed of said anode and a cathode adapted to supply direct current of varying potential to said motor from said source 01' alternating current, said potential variations of the direct current being dependent upon the grid' potential of said tube, a Wheat- 5 stone bridge having two of its terminals connected to the source of energy and having two of the legs that are connected in series of equal resistance, the other two legs that are connected in series having one leg provided with means 10 for manually varying the resistance and the other leg provided with electrical time-limit means for automatically varying the resistance a given value during a substantially fixed interval of time and means responsive to the potential variations 15 thus efiected at the other terminals of the bridge to vary the grid potential of said tube. 15. A. control system for an electric motor, in combinationfl'a source of energy, means for connecting the motor to the source of energy, speed 20 control means for the motor, thermionic means independent of said speed control means for controlling the acceleration of the motor, and timing means, operable during a substantially definite time interval, adapted to control the ther- 2 mionic means.

16. In a control system for an'electric motor, in combination, a source of alternating current, a motor, a grid-controlled electric discharge device Ior supplyingvarying amounts of direct cur- 3 rent to said motor from said source of alternating current, and time-limit means, including a capacitor and a grid-controlled electric discharge device, adapted to change the operating characteristics of said first named electric discharge device by a given amount during a given interval or time to thus govern the rateof accelerati on of said motor.

17. In a control system for an electric motor, in combination, a source of alternating current 40 energy, a direct current motor, a grid-controlled electric discharge device interconnected with said source of alternating current and said motor and adapted to supply direct current to said motor from said source of alternating current, a 65 phase-shifting circuit-arrangement for said electric discharge device whereby the effective direct current voltage impressed on said motor is vamotor at will, and a timing device including a grid-controlled electric discharge device and capacitor interconnected with each other, said timing device'controlling the operating characteristics of said phase-shitting circuit-arrangement to control the rate of acceleration to the speed selected for said motor by. said phase-shifting circuit-arrangement.

LAWRENCE R. QUARLES. 

